By Harvey Leonard, Chief Meteorologist, WCVB-TV

Our last two winters could not have been more diametrically opposed. Two years ago, during the winter of 2010-11, 81 inches of snow fall in Boston (average is 43.8), including an intense 6 ½ week period of snowstorm after snowstorm along with unabated cold.

The result: many roof collapses, along with numerous weather related hardships and inconveniences.

But, last winter (2011-2012) we experienced the reverse -- only 9.3 inches of snow (one of the least snowy ever) and temperatures were far above average. In fact, it was one of the warmest winters on record.

Interestingly enough, if you take the average snowfall for these 2 winters (45.1 inches), it turns out to be almost our normal average (43.8).

Perhaps even more amazing, there is a meteorologist, for whom I have a great deal of respect, who was able to accurately predict the weather for these past 2 winters. His name is Dr. Judah Cohen, and he is Director of Seasonal Forecasting at AER (Atmospheric and Environmental Research, Inc.) in Lexington, Mass. Cohen specializes in forecasting what the next few months will be like, while I specialize in what the next week or so will be like.

That is why I am comfortable deferring to Cohen when it comes to seasonal forecasting.

Cohen has let me in on some of the research he has been conducting. He has found the amount of snow cover in Siberia during the month of October to be one of the major indicators of how cold our winter will be.

When October snow cover is above average in Siberia (such as in 2010), our winter temperatures are usually colder than normal (think of it as a refrigerator door opening, and the cold air spilling and spreading out), and when October snow cover in Siberia is below average (such as in 2011), our winters are usually milder than normal.

This past October (2012), snow cover in Siberia was above average, and it is one of the main reasons why Cohen is expecting our winter to be colder than normal.

But, predicting winter snowfall is much more difficult, because the slightest temperature change during a major storm could cause snow to be rain or vice versa, and Cohen actually doesn’t make winter snow predictions.

But he does make winter precipitation predictions. One of the factors Judah looks at is the jet stream.

Usually during winter there are two jet streams that we look at. One is the northern jet stream, which steers the cold air. The other is the southern jet stream, which steers the moisture (storms).

When these two jet streams interact with each other, big winter storms can result. However, when they stay separate, our winter weather is not as cold or as stormy.

Last winter, the two jet streams remained separate. We call that “zonal flow,” because each zone is minding its own business. The arctic cold stays locked up north and doesn’t often penetrate strongly into the U.S. And southern storms move from west to east and are not steered up the East Coast. So, we stay relatively mild and storm-free.

But, sometimes strong blocking high pressure builds across the higher latitudes, especially over Greenland. When that happens, the northern jet stream gets suppressed to the south, allowing the cold, arctic air to penetrate into the Eastern United States.

Plus, the northern jet stream can interact or merge with the southern jet stream and allow southern storms to be steered up the East Coast, where they bump into the cold air to produce snowstorms. That happened a lot during the winter of 2010-2011.

This winter, Cohen sees signs that this blocking pattern will develop at times, so even though his forecast is for near normal precipitation, Cohen feels the chance of above average snow is greater than the chance of below average snow.

So, in summary, as of now, expect a somewhat colder than average winter, with at least average snowfall, and possibly somewhat above average snowfall.